This invention relates to an ink-jet printer which performs printing by jetting ink onto a sheet of paper held on a rotary drum as a printing medium.
Recently, personal computers of high performance and low cost have been readily available, and are widely spreading rapidly. With this spread, demands for color printers also increase. For personal use, various types of ink-jet printers have been developed for color printing.
Conventionally, for example, an ink-jet printer capable of printing 500 sheets or more continuously is known. The ink-jet printer includes a rotary drum which rotates at a constant circumferential speed and a print head for jetting color inks onto a paper sheet held on the peripheral surface of the rotary drum. The paper sheet is loaded on the rotary drum from the front side thereof and printed in a state wound around the rotary drum. After printing, the paper sheet is removed from the drum and discharged to the rear side of the rotary drum.
The print head includes nozzle units arranged along the peripheral surface of the rotary drum to print an image in yellow, cyan, magenta and black, for example. Each nozzle unit has a plurality of ink-jet nozzles aligned across the paper sheet in the main scanning direction parallel to the axis of the rotary drum and jets ink from the ink-jet nozzles to print an image over all the paper sheet while the paper sheet moves in the sub-scanning direction perpendicular to the main scanning direction with the rotation of the drum.
The above-described conventional ink-jet printer requires a long printing time to perform continuous printing. The rotation of the drum stops each time the paper sheet is loaded thereto or removed therefrom, so as to prevent a print head from being damaged due to a rise of the paper sheet. It is considered that the printing time can be shortened, for example, by increasing the rotational speed of the rotary drum. However, this makes it difficult to quickly stabilize the rotational speed of the drum, and also increases the load on a motor for driving the drum. In light of these reasons, an increase in the rotational speed of the drum is restricted.